"Photodynamic Therapy" (PDT) is a term for a common method for the treatment of cancer and in humans and in animals. There are thee types of devices useful in PDT: The fiber optic cylindrical diffuser or "line source" is one of these types and it is to the cylindrical diffuser that this invention is directed.
The fiber optic cylindrical diffuser is characterized by a cylindrical light scattering pattern symmetrical with respect to the central axis of the optical fiber. Such apparatus has been made with an optical fiber having an exposed core portion at one end with a scattering medium coated on the exposed portion. The apparatus also includes an open end tube adhered to the scattering medium on the clad portion. Apparatus of this type was subject to breakage in use and was limited in the amount of optical energy the apparatus was capable of transmitting safely.
U.S. Pat. No. 5,074,632 issued Dec. 24, 1991, discloses a cylindrical diffuser which overcomes the above defficiencies of some extent. The apparatus of that patent includes a colorless sleeve member which adheres to the clad portion of an optical fiber without touching the exposed core portion of the scattering medium coated on that portion. In a preferred embodiment, the sleeve member has a core head which is at a angle to the flat end of the exposed core portion of the fiber and is spaced apart from that end defining an air filled cavity therebetween. In another embodiment, the core head is open.
It has been found that the light distribution patterns produced by cylindrical diffusers of the above-noted types are insufficiently uniform at distances close to the fiber (the near field) and only moderately better at distances further from that (the far field). In addition there is an increasing need for greater uniformity, increased laser power delivery and mechanical strength in such fiber optic diffusers.